Correct procedure for reading BLE characteristic values.

[MSuva.1]

I am currently trying to read the value from a characteristic after detecting that the user has written to it.

 

I am calling aci_gatt_read_char_value() which is returning 0 (BLE success). From here I am expecting an event which triggers the aci_att_read_resp_event() function but I am not seeing that get called.

However, I am seeing that the Custom_STM_Event_Handler(void *Event) gets called directly after I call this function and the event code is: 

I'm not sure what the issue here exactly. Should I be setting a flag and then calling the read function elsewhere? Or is there some other issue with my setup?

Thanks very much

Maks

[Remy ISSALYS]

Hello,

When you received the ACI_GATT_ERROR_RESP_EVENT event, which error code do you have?

Best Regards

[MSuva.1]

Hi Remy,

The ACI_GATT_ERROR_RESP_EVENT seems to have cleared up by itself. I'm not sure i'm going about this the write way at all. Is there a correct way to access the value that has just been written by the client?

 

When the client writes to the variable the ACI_GATT_WRITE_PERMIT_REQ_VSEVT_CODE is triggered. Is it correct that I am calling the read function here? Or is there just some variable I can read to see what new value has been written to the characteristic?

Thanks very much,

Maks

[Remy ISSALYS]

Hello,

Before calling the read function, you should respond to the write permit request with the write response command. When ACI_GATT_WRITE_PERMIT_REQ_EVENT is received, the application has to check whether the value being requested for write can be allowed to be written and respond with the command ACI_GATT_WRITE_RESP. You can refer to STM32WB_BLE_Wireless_Interface.html documentation to have more detail about ACI_GATT_WRITE_PERMIT_REQ_EVENT and ACI_GATT_WRITE_RESP.

Best Regards

[MSuva.1]

Hi,

I've removed these from the GATT attributes now:

I want the client to write without me having to give any sort of response and I want to be able to read what they wrote immediately.

I've removed the "wait for response" GATT attributes.

I assume this removes the necessity for me to send any sort of "ACI_GATT_WRITE_RESP"?

What is the step after this to access the newly written value?

Thanks again

[Remy ISSALYS · Accepted solution]

Hello,

Yes, with the modification you don't have to send the write response. So, when you received the write on server side the ACI_GATT_ATTRIBUTE_MODIFIED_VSEVT_CODE event is generated and you can perform your action according to the write value received. You can look BLE_p2pServer example available in STM32CubeWB package, to see how manage the write (see PeerToPeer_Event_Handler function p2p_stm.c file).

Best Regards

[MSuva.1]

This explanation and example have fixed my issue. Thanks very much Remy, much appreciated 🙂